Motion-transmitting system in a timepiece



March 1, 1966 G. RAVAL MOTIONTRANSMITTING SYSTEM IN A TIMEPIECE Filed July 10, 1964 2 Sheets-Sheet 1 INVENTOR Gaston Ra al ATTORNEY March 1, 1966 cs. RAVAL MOTION-TRANSMITTING SYSTEM IN A JIIWEFPIECE 2 Sheets-Sheet 2 Filed July 10, 1964 lbIfVENTOR 35 on V8 M2 mwr ATTORNEY United States Patent 3,237,461 MOTION-TRANSMITTING SYSTEM IN A TIMEPIECE Gaston Raval, La Neuveville, Switzerland, assignor to Omega Louis Brandt & Frere S.A., Bienne, Switzerland Filed July 10, 1964, Ser. No. 381,838 Claims priority, application Switzerland, July 16, 1963, 8,873/ 63 7 Claims. (Cl. 74-96) This invention relates to a motion-transmitting system between an oscillating member electrically sustained in oscillation and the wheelwork of a timepiece, comprising a transmission lever actuated by a driving element of the said oscillating member, said driving element being engaged within a fork of the transmission lever in a position symmetrically opposite the open side of the fork when the oscillating member is in its neutral rest position. In electrieor electronic timepieces the classical function of the escapement, that is the transmission of the driving energy-to-t'he' balance wheel for sustaining its oscillation, is accomplished by an electro-mechanical driving system. Under such circumstances the transmission between the oscillating member, for instance the balance Wheel, and the wheelwork of the timepiece is a simple motiontransmitting system serving for transmission of energy from the balance wheel to the wheelwork and hands respectively.

It is Well known that the stability of the frequency of oscillating members of timepieces, such as balance wheels, depends on the Q-factor of the oscillating system. Since energy is withdrawn from the oscillating member for driving the wheelwork and hands of the timepiece, care must be taken to withdraw the said driving energy under the most favourable conditions in order not to affect the Q-factor and consequently the stability of the oscillating system. The kinetic energy withdrawn should be as small as possible. Moreover, the driving energy should be withdrawn within a period of time as short as possible as compared with the oscillating period of the oscillating member and this period of time should coincide as closely as possible with the passage of the oscillating member through its neutral position that is with the maximum speed of the oscillating member. For meeting with these conditions the amplitude of displacement of the transmission lever should be small compared with the amplitude of the oscillating member and the mass of the driven system should be very small.

The motion-transmitting system according to this invention is adapted to fulfil the above conditions and it is perfectly suitable for use with an electrically sustained oscillating member. The motion-transmitting system according to this invention is broadly characterized in that the arc of curvature of the said fork includes an angle exceeding 180 and the shaft of the oscillating member is entirely engaged within the fork in an eccentric position relatively to the arc of curvature of the fork, and the said driving element has the shape of a crescent.

The characteristics and advantages of this system will now be explained in detail with reference to an embodiment of the invention shown by way of example in the attached drawings wherein FIG. 1 is a top view of the system,

FIG. 2 is a section taken along line II-II in FIG. 1 and FIGS. 3-5 illustrate different characteristic positions of the system.

The electrically driven balance wheel is not shown in detail. A plate 2 is fixed on the shaft 1 of the balance wheel, the said plate 2 comprising a driving element or hook 3 in the shape of a crescent. When the balance wheel is in its neutral rest position (FIGS. 1 and 3) the hook 3 is symmetrically engaged within a fork 4 comprising a cylindrical portion 5 having a gap or open side 6. The fork 4 is fixed on a transmission lever 7. The end of the lever opposite to the fork 4 is a fork of which the arms 8 and 9 are pivoted by separate pivot pins 10 and 11. The fork arms 8 and 9 enclose a pawl wheel 12 gearing in a manner not shown in the drawing with the wheelwork driving the hands of the timepiece. A pawl 13 is mounted on lever 7. The supporting spring 14 of a stop-clock 15 is fixed at a portion 16 fixed in a portion 17 of a bridge 18. The bridge 18 has a slit 19 so that portion 17 is connected to the bridge 18 by a relatively narrow elongated portion 20. By means of adjusting screws 21 and 22 the bridge portion may elastically be deformed for adjustment of the position of portion 17 and of the stop-click 15 respectively.

The driving hook 3 has an outer surface of cylindrical shape and of which the diameter is at least approximately equal to the diameter of the inner cylindrical surface of the curved portion 5 of the fork 4. The center of curvature of the inner surface of the fork is displaced upwardly in the direction of the common plane of symmetry of the fork and of the hook 3 as seen in FIG. 1 relatively to the axis of the balance wheel.

When the balance wheel and the fork are in their rest positions as shown in FIGS. 1 and 3, the fork is in a symmetrical position relatively to the axis of the balance wheel. The driving hook 3 is in a symmetrical position relatively to the fork so that the outer cylindrical surface of the hook 3 does not contact the inner cylindrical surface of the curved portion 5 of the fork. When the balance wheel starts to oscillate with a relatively small amplitude the hook 3 will first oscillate without touching the inner surface of the fork. This feature of the transmitting system is important for the starting abilities of an electrically driven balance wheel because no energy is Withdrawn by the motion-transmitting system for small amplitudes whereby starting of the oscillation of the balance wheel is appreciably facilitated and improved. At greater amplitudes of the balance wheel the outer cylindrical surface of the hook 3 touches the inner cylindrical surface of the fork whereby the fork is displaced to the right or left according to the rotating direction of the plate 2. The fork and transmitting lever 7 are accelerated relatively rapidly and the system is so disposed that the maximum amplitude of the fork and lever 7 is obtained for amplitudes of the balance wheel of 60 or more. The maximum displacement of the fork and lever 7 is shown in FIG. 4. This figure illustrates that the width of the gap 6 of the fork and the width of the hook 3 are so coordinated that the hook is able to leave the fork through its gap. FIG. 4 illustrates the one extreme position of the hook 3 at normal amplitude of the balance wheel in the order of 200. For amplitudes appreciably exceeding 200 the one extremity of the hook 3 will abut against the outer surface of fork portion 5 as shown in FIG. 5. Under these conditions the one extremity of the hook 3 abuts against the outer surface of the fork and the inner surface of the fork abuts against the tube of plate 2 mounted on shaft 1 of the balance wheel. The extreme positions or amplitudes of the balance wheel and of the lever 7 are thus positively limited. In this way the maximum amplitude of the balance wheel is limited to about 265. This limitation of the amplitude of the balance wheel is of particular importance for electrically driven balance wheels in order to avoid undesired supplemental operation of the electromagnetic or dynamic driving system in the extreme positions of the balance wheel.

The complete disengagement of the transmitting system from the balance wheel for small amplitudes of the latter has another advantage. In most of the known systems wherein the balance wheel is also mechanically coupled with the transmitting system for small amplitudes an additional factor of elasticity and inertia is added to the elasticity of the spiral and the inertia of the balance wheel so that the natural frequency of the oscillating system may appreciably be modified, whereby starting up of the oscillation is rendered more difficult. This difficulty is entirely avoided by the transmitting system according to the present invention.

What I claim is:

1. A motion-transmitting system comprising a shaft for an oscillating member, a driving element carried by said shaft, a transmission lever actuated by the driving element of the said oscillating member, said driving element being engaged within a fork of the transmission lever in a position symmetrically opposite the open side of the fork when the oscillating member is in its neutral rest position, the arc of curvature of the said fork including an angle exceeding 180 and the shaft of the oscillating member being entirely engaged within the fork in an eccentric position relatively to the curvature of the fork, and the said driving element having the shape of a crescent.

2. A system according to claim 1, the said fork and the said driving element being so disposed that the driving element is adapted to leave the fork through the open side of the latter.

3. A system according to claim 2, wherein the said driving element and the said fork are so disposed that the movement of the fork is always limited by the driving element and by the shaft of the oscillating member.

4. A system according to claim 1, wherein the oscillating amplitude of the oscillating member is limited by the fork.

5. A system according to claim 4, wherein the outer surface of the fork forms an abutment for the driving element.

6. A system according to claim ll, wherein the inner surface of the fork and the outer surface of the driving element are of cylindrical shape and of substantially equal diameter. I

7. A system according to claim 1, wherein the said transmission lever is pivotably mounted at one of its ends and carries the said fork at its other end.

References Cited by the Examiner UNITED STATES PATENTS 2,789,411 4/1957 Ensign 'et al. rm. 74- -12'6 X BROUGHTON G. DURHAM, Primary Examiner. I J. A. MARSHALL, Assistant Examiner. 

1. A MOTION-TRANSMITTING SYSTEM COMPRISING A SHAFT FOR AN OSCILLATING MEMBER, A DRIVING ELEMENT CARRIED BY SAID SHAFT, A TRANSMISSION LEVER ACTUATED BY THE DRIVING ELEMENT OF THE SAID OSCILLATING MEMBER, SAID DRIVING ELEMENT BEING ENGAGED WITHIN A FORK OF THE TRANSMISSION LEVER IN A POSITION SYMMETRICALLY OPPOSITE THE OPEN SIDE OF THE FORK WHEN THE OSCILLATING MEMBER IS IN ITS NEUTRAL REST POSITION, THE ARC OF CURVATURE OF THE SAID FORK INCLUDIN AN ANGLE EXCEEDING 180* AND THE SHAFT OF THE OSCILLATING MEMBER BEING ENTIRELY ENGAGED WITHIN THE FORK IN AN ECCENTRIC POSITION RELATIVELY TO THE CURVATURE OF THE FORK, AND THE SAID DRIVING ELEMENT HAVING THE SHAPE OF A CRESCENT. 